The present invention relates to a process for producing a polarizing ophthalmic lens which is adapted to the eye/head behavior of a wearer of this lens. It also relates to the lens itself, which comprises zones associated with polarizing filters having different orientations. These zones are determined as a function of the wearer's eye/head behavior.
Natural light is unpolarized: the electromagnetic waves of which it is composed vibrate in all directions. David Brewster, from 1811 onward, demonstrated that for a certain incidence, monochromatic light which is reflected on a transparent surface is 100% polarized. Brewster's law stipulates that the direction of polarization of the reflected wave is parallel to the reflection plane. Thus, the reflection of light on a horizontal plane is polarized horizontally. Polarizing ophthalmic glass has been designed in response to these physical properties of reflective light. Glass whose direction of polarization is horizontal selectively filters the light rays which are derived from the reflection on horizontal transparent surfaces. This glass is particularly effective for eliminating undesirable reflections off bodies of water, off flooring surfaces, off sand or off snow. Nevertheless, horizontal reflective surfaces do not form the majority of the potential sources of glare. Thus, light which is reflected off the window panes of a building or a car is, contrary to the preceding case, vertically polarized.
Certain characteristics of the landscape present in the field of vision of a person are particular to an urban environment. The urban environment has, in particular, numerous vertical reflective surfaces, such as, for example, the glazing panels of buildings. These vertical walls generate reflections whose intensity may be sufficient to cause glare. Such glare is a source of discomfort, but it may also be a source of danger in certain circumstances. This is especially the case for a driver of an automotive vehicle or of a motorbike, for example.
When an individual visually explores his environment, his eyes and his head move in order to guide his gaze to the area of interest. The spatial and time coordination of the eye and head movements has been the subject of numerous research projects. In particular, document FR 2 863 857, in the name of the Applicant of the present patent application, describes a process for measuring the amplitude of the eye and head movements of an ophthalmic lens wearer. It appears that the strategy used for exploring his environment is specific to each individual. When a target is presented in the peripheral visual field, the relative participation of the head and the eyes varies from one subject to another: for certain people, who are called “head movers”, the major part of the movement will be carried out by the head; for other people, who are called “eye movers”, the eyes will be mainly used to bring the gaze to the target (Afanador, et al., 1986; Fuller, 1992). The propensity to move the head or the eyes most is measured by a gain obtained by dividing the angular deviation of the head by the angular eccentricity of the target. A gain of 1 means that the observer has not moved his eyes and that all the movement necessary to place the gaze on the target was carried out by the head; this is then a subject of the “head mover” type. A gain of 0 characterizes, on the other hand, an “eye mover” observer. But individuals are not distinguished by the two “head mover” vs “eye mover” categories. This is because there is a continuum of behaviors between the two extreme behaviors described previously (Fuller, 1992).
One object of the present invention is to provide a customized protection of the visual function of an ophthalmic lens wearer, against the glare which is caused by reflections of light from reflective surfaces, by taking into account the individual eye/head behavior of each lens wearer.